The purpose of this renewal request is to guarantee the continuance of a series of comparable surveys of drug use among junior and senior high school students in San Mateo County, California. Surveys using similar basic formats have been conducted annually in 1968-1974. The surveys, in cooperation with the office of the County Superintendent of Schools, were administered across the County to all students in participating schools. Private, parochial and public schools are included. Levels of use of alcoholic beverages, amphetamines, LSD, marijuana, tobacco, barbiturates and heroin are surveyed. The surveys include approximately 30,000 responses, each of which permits significant differences in patterns of use between sexes and grades. It is also possible to show significant differences in level of use by class-sex groups over time. Every effort is made to enforce comparability between annual surveys. Seven comparable surveys makes it possible to trace the level of use of various drugs in a population over time. Such controlled observations can make a contribution toward setting up a general epidemic model for the growth of drug use in a particular population which could have important implications in long-range strategies for control. The model presents parallels to a chronic disease, such as tuberculosis. Also of interest are multiple patterns of use.